What is a longitudinal survey?
A longitudinal survey obtains information from the same respondents at multiple points in time. A cross-sectional survey, by comparison, obtains information from respondents at a particular point in time. Cross-sectional surveys that are repeated monthly, quarterly, annually, or with some other periodicity usually include a different sample of respondents each time they are administered. Many of the repeated cross-sectional surveys sponsored by BLS include a mix of new and experienced respondents each time they are administered, rather than selecting an entirely new sample for each administration. Longitudinal surveys like the NLSY79 and NLSY97 are useful for studying changes that occur over long periods of time, such as the number of job changes or unemployment spells that people experienced over some segment of their lives, the number of times they moved to a different county or State, or the number of years in which their family income was below the poverty threshold. For a variety
